An image forming apparatus that forms an image using a decolorable toner, the color of which can be erased, is known. The decolorable toner can be used like a conventional non-decolorable toner when forming the image. When the image is formed, the image formed by the toner is fixed on a sheet of paper by heating a fixing unit to a certain temperature, e.g., 100° C., and conducting the heat to the toner. The color of the decolorable toner can be erased by heating the fixing unit to a certain temperature, e.g. 120° C.-150° C., at which the color of the toner disappears, and conducting the heat to the toner. Thus, the temperature at which the color of the decolorable toner disappears is higher than the temperature at which the decolorable toner forming an image is fixed on the sheet of paper.
If image forming is continuously carried out, the temperature of the fixing unit may reach a temperature at which the color of the decolorable toner disappears. In addition, when the apparatus is switched to an image forming mode from an erasing mode, if the apparatus has both functions of image forming and image erasing, the temperature of the fixing unit may not fall to the temperature for forming the image soon enough. In such situations, images cannot be formed on the paper, and the apparatus has to wait until the temperature of the fixing unit drops sufficiently. This waiting time can be very inconvenient for the user.